Ferrous alloys and rotor forgings for gas turbines



Patented Nov. 9, 1948 UNITED ,STATES PATENT ALLOYS AND ROTOR FORGINGSFOR GAS TURBINES FERROUS F F l C E Adolph 0. Schaefer, WhitpainTownship, Montgomery County, Pa., assignor to The Midvale Company,Philadelphia, Pa., a corporation of Delaware No Drawing.

, 1 Rotorforgings for gas turbines of jet propulsion units of airplanesand for other gas turbine application must be made of materialpossessing the characteristics of weldability, of machin characteristicsas sensitivenessto small variations in manufacture, which frequentlyoccur in the same technique; or they are inclined to show both externaland internal defects in ingots as well as in the forgin s made fromthem, which may not appear on the surface at any stage of manufactureand can only bediscovered by skiagraphic or supersonic test; or they maybe difficultly forgeable; or may lack hot strength or ductility atoperating temperature.

V In several of the alloys some of the chemical elements apparently havea tendency to form areas of local enrichment instead of enteringuniformly into the general alloy. Such nonhomogeneous areas have theeifect of embrittling .the article in which they exist, so that onoverspeed bursting tests there may be Wide variations in the speed atwhich failure occurs. These compositions are also prone to surfacedefects entail ing a highpercentage of loss in forging.

With the object of producing a ferrous alloy which would be more readilyfabricated, would be free from the defects above mentioned, would havesuflicient strength at working teperatures,

and possess such improved ductility and soundness as would give moreuniform performance in operation, many thousandsof dollars have beenexpended under my direction in testing a wide variety ofcompositions,which have covered the range of elements in general use for such ferrousalloys, in an effort to determine Whether any combination of them wouldexhibit thev desired characteristics. This involved a determination ofwhat alloys are essential, which are non-essential or objectionable, andthe limitswithin which the absolute and relative proportions of theselected elements should be present. I finally found that an alloy ofthe following composition would achieve the desired result, besideshaving other desirable and important characteristics:

Application August 29,1945, Serial No. 613,423

4 Claims. (c1. 75 -12s) As is well understood by those skilled in theart, it is generally not possible to secure an exact composition, andthat in the endeavor to obtain my preferred composition the result islikely to vary within approximately the following limits:

Percent C 1 to 15 Mn 4 to 6 Si 4 to 6 Ni 11 to i 12 Cr 18. '75 to 19.75W 3 to 3. 5 Cb l to 1.5 N2 About 15 Fe 62 to Deviations from the abovepercentages, although within rather limited ranges, are permissiblewithoutseriously impairing the qualities of the alloyed steel. Suchqualities are retained, with but moderate impairment in degree, incompositions not within the above limited ranges but within thefollowing broader ranges:

Percent C 05 to 3 Mn 3 to 1. 0 Si 3 to l. 0 Ni 9 to 15 Cr 15 to 25 W 2to 5 Cb 5 to 2 N2 05 to 3 Fe (balance) 52 to '72 While the minimum ofchromium and the maximum of nickel within the above broader ranges areapproximately the same, the percentage of chromium in any givencomposition should substantially exceed the percentage of nickel.

Similarly, while the minimum of tungsten approximates the maximum ofcolumbium within the above broader ranges, the percentage of tungsten inany given composition should substantially exceed the percentage ofcolumbium.

Ferrous alloys embodying my invention will not be entirely free fromimpurities such as phosphorous and sulphur, but the percentage of theseimpurities should be kept low and preferably should not exceed about.03% of either.

While a composition embodying my invention does not necessitate theabsolute exclusion of any alloying ingredient in addition to thosenamed, I am aware of no other element that can be added that willimprove the composition, and the addition of any one of most commonalloys of steel in any substantial proportion will, I believe,appreciably impair the desirable qualities of the specified composition.For example, the addition of molybdenum in any percentage approachingthat of the prescribed percentage of tungsten is dis- The presence of aslight D rcientageof tantalum whether introduced in the f-errocolumbiumor in-' tentionally, is without utility, as.wou1d also be the additionof titanium, of which the-presence iniany substantial proportion isdetrimental. Therefore, aside from the elements specified, the remainderof the composition is preferably nearly all iron.

A ferrous alloy embodying my invention is readily fabricated withoutundue loss in casting or forging operations. The material hasbeencast ina number of induction furnaces, and in one large arc furnace, heats withexcellent results and airsoduction of sound forgings several times thatsecured in another composition used for the same purpose with Which 1have had several years experience.

Investigation of cut-up Wheel forgings made of known suitableferrous-alloys offer-valuable advantages -for this material.

Another quality of my improved alloy which is of great importance is theremarkable uniformity in physical properties of the forgings made fromit. This is in striking contrastto the results obtained from suchcompositions as are sensitive to slight variations in manufacturingtechnique.

if improved ,ferrous alloy is readily fabricated and the productextremely uniform in quality, as stated. Five 18 /2" diameter wheels ofthis material have been overspeeded until they "burst, and the range ofbursting speed wa only afrom 22,610 R. P. M. to 23,350 R. P. M.

My claims with regard to this alloy are thatit has:

11. Sufficient strength at the temperature range of operation of gasturbines.

2. Greater flexibility in fabrication both :in casting and forging, thanthe ferrous alloys now in use for this purpose.

manufacture of rotorforgings for gas turbines, said alloy containingcarbon .05 to less than .3 per cent, manganese over .3 and less than oneper cent., silicon over .3 and less than one per cent.,nicke1,0Ver.-'9't0' less than per cent,. chromium over 15, to less than25 per cent., tungsten over 2 .to less than 5 per cent., columbium over.5 to less "than-.2 per. cent and nitrogen over .05 to less than..-.3.per cent., with a maximum of phosphorus and sulphur not over.103'per cent. each, substantially all of the remainder being iron whichcomprises the majorproportion of the alloy, the percentage Considerablesavings in material, labourand equipment as a result of the decreased:loss 0 forgings in process.

Higher ductility than materials heretofore used, which permitsanautomatic distributioniof stresses to a greater degree than is possiblein materials of equal strength and less ductility.

' 5. Greater uniformity of product because of the :less sensitive natureof the alloy. 1

6. More uniform properties in parts of-widely of chromium substantiallyexceeding the percentage of nickel and the percentage of tungstensubstantially exceeding the percentage of columbium; said compositionbeing characterized by great ease in casting andiorging,adequatestrength at the temperature rangeof operation of gasturbines,high ductility permitting of maximum automatic distribution of stresses,and uniformity of product particularly in parts of widely differentthicknesses.

2. A ferrous alloy containing carbon .10 to .15

per cent.,- manganese .4 to .6 per cent., silicon .4 to .6-per cent.,nickel 11,to 13'per cent., chromium 18.5 to' 19.75 per cent.,, tungsten3. to'3.5 per cent., columbium .8 to 1.5 per cent., nitrogen .10 to .20per. cent., with a maximum of phosphorous and sulphur not over .03 percent. each, substantially all of the-remainder, about 62 to 65 percent,'beon, the percentage of chromium substantially exceeding thepercentage-of nickel and the percentage of tungsten substantiallyexceeding the percentage of columbium; said c-ompositionbeincharacterized by great ease in casting and forging, adequate strength atthe temperature range of operation of gas turbines, high ductilitypermitting of maximum automatic distribution of stresses, and uniformityof product particularly inparts of Widely different thicknesses.

'3. A-rotor forging for gas turbines having the composition specified inclaim 1.

"4. A rotor forging for gas turbines having the composition specified inclaim 2.

ADOLPH O. SCHAEFER.

"REFERENCES CITED The following. reference s areofv record. in the .fileof this patent:

OTHER, REFERENCES Eifects of Special Alloy Additions to'Stainless Steel.Franks; published in October 1938 by the Electro' Metallurgical'C-o, NewYork city.

